Exam 1 - Lecture 3 Flashcards
Two components that determine cardiac output:
health of heart and health of system
increase of resistance to venous return will cause
less venous return and less cardiac output
e.g. Right atrial pressure 0mmHg has 5L/min of venous return at Psf of 7, but if RA pressure is +4 its 2.5L/min
If right atrial pressure increases, what needs to increase in order to raise venous return instead of lowering it?
Higher Psf. If it stays the same, then the delta P falls lower than 7 and it would decrease venous return.
Why is making the right atrial pressure negative not as effective as raising the right atrial pressure + also increasing Psf?
if its negative it can only go up to 6L/min bc the veins would collapse from the negative pressure.
If body needs to enhance CO for a marathon, it chooses to
Change the Psf!!!!
by tightening arteries to improve blood flow to muscles,
mesenteric arteries clamp down to shut down digestion
Increase BP
Increase venous constriction to raise Psf the most to improve blood returning to heart
Primary obstacle to blood returning to heart would be
Chest full of air can compress the vena cavae and return in less venous return, such as during positive pressure ventilation. Counter this by tightening up veins with phenylephrine or more air per breath.
What medication can tighten up veins to produce more venous return to heart?
Phenylepherine
Where does majority effect of phenylephrine work?
Tightens up the veins more than arteries, and only has to tighten up them a little bit
A hypoeffective heart will move the cardiac output curve to the
right
A hypereffective heart will move the cardiac output curve to the
left
IF someone has a heart problem, what happens to their CVP, and why?
increased and its because the heart cant pump it all out
If the heart is weakening, the catecholamines step up. but if its a long term issue, its scaled back and replaced by
volume retention and blood expansion at the kidneys. Norepi and epi increase water retention as well.
What is the max cardiac output if we maxed venous return but didnt do anything to the heart?
13L/min
When the body wants to increase CO, the main thing the body adjusts is
venous return
Output of the heart is geared by the
metabolic rate
Conditions that increase metabolic rate/cardiac output (from highest increase of CO to lowest increase)
Beriberi, AV shunts, hyperthyroidism, Anemia, pulm disease, pagets disease
Conditions that decrease metabolic rate
Removal of arms and legs, hypothyroidism (lowest metabolic demand).
When cardiac output is reduced due to less metabolic demand, what happens to peripheral resistance?
increased to allow less blood flow to tissues.
When cardiac output is increased due to more metabolic demand, what happens to peripheral resistance?
Decreased to allow more blood flow to tissues.
Beriberi
Vit B1 deficiency, makes cells much less efficient and need to use more energy now.
not common in US, usually only third world countries
Why does vascular resistance reduce with AV shunts?
its one more route for the blood to take, reducing resistance
Cardiac output is tightly linked to
oxygen consumption
Dinitrophenol
old weight loss drug that would drive up metabolic rate
need nervous system to cooperate in order to boost cardiac output on this chart (????)
How does dinitrophenol help with blood pressure?
keeps blood pressure from crashing.
arteries dilate and veins will constrict to produce more venous return and cardiac output